Fluorescent whitening agents



2,715,630 Paftented Aug. 16, 1955 FLUORESCENT WHITENING AGENTS Mario Francesco Sartori, Monroe Park, Del., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Application November 16, 1954, Serial No. 469,293

8 Claims. 01. 260304) This application is a continuation-in-part of my copending application Serial No. 408,599, filed February 5, 1954, now abandoned. The invention relates to the production of novel organic compounds which are useful as whitening agents for fibrous material such as textiles or paper. It is an object of this invention to produce compounds of the above general nature, but which are characterized further by bleach fastness, by correct shade of fluorescence, and by good build-up qualities. Additional objects and achievements of this invention will appear as the description proceeds.

The art of whitening or brightening textile fiber and paper is of relatively recent development. It has been found that fibrous materials which normally have a dull. yellowish cast when in the white, unbleached state, hecome whiter and brighter if treated with agents which fluoresce under ultraviolet light. Presumably the action of the ultraviolet rays present in ordinary daylight is suflicient to excite these agents upon the fiber to emit fluorescence which overcomes the undesirable tinge of color in the unbleached fiber. Best results are obtained when the shade of fluorescence is complementary to that of the unbleached fiber, so that the colors will cancel out each other. Since the most common ofi-white shade of 1mbleached cellulosic fiber is yellowish, the most desirable shade in a fluorescent is blue.

Another very important demand developed by the trade is bleach fastness. Inasmuch as the aforementioned fluorescent agents are generally incorporated into soap and synthetic detergents, which are packaged and marketed for household use, and inasmuch as in household practice laundered articles are often subjected to bleaching with various agents, for instance hypochlorites, it is essential that the fluorescent transferred from the detergent to the fiber shall not be destroyed by the action of bleach. Unfortunately, most of the fluorescent agents now on the market, and having the desirable blue shade, are weak in respect to this qualification of bleach resistance.

In addition to the above two primary qualifications, an agent to be commercially successful must be capable of being synthetized economically from readily available materials, and must have suflicient fluorescent power (often referred to as tinctorial strength?) to give the desired eflect at a minimum cost. It is also desirable that the agent should have good build-up qualities; in other words, repeated treatments with a bath of the same concentration, should continually increase the whiteness of the treated fabric, up to a maximum. The agent must also have aflinity for the fiber that is to be treated and must possess sufficient Water-solubility to be applicable from an aqueous bath in the concentrations that would normally be used.

Now according to this invention new chemical compounds are synthesized which satisfy to an excellent degree all the aforegoing qualifications. The novel compounds of my invention may be defined by the general formula XII wherein Y designates a member of the group consisting of O, S and NH (oxygen, sulfur and the mine radical), X is a sulfo group, while n stands for an integer not greater than 2. 1

These compounds may be synthesized by tetrazotizing a member of the group consisting of 6-amino-2(p- .aminophenyl) benzoxazole, 6-amino-2(p-aminophenyl) benzthiazole and 6-amino-2(p-aminophenyl benzimidazole, then coupling in acid medium to two moles of an aminonaphthalene monoor di-sulfonic acid wherein the NH2 group is located in one of the positions 1 and 2 while the other of said two positions is free, and oxidizing the resulting bis-orthoaminoazo compound to the corresponding di(naphthotriazole) derivative. The latter step may be achieved by heating the bisorthoaminoazo compound in an aqueous solution of cupric ammonium sulfate or of sodium hypochlorite until the color of the intermediate disazo dye has disappeared. The product is then recovered in the desired physical or chemical form, for instance in the form of its sodium, potassium or ammonium salt.

If it is found that the aqueous reaction mass, prior to salting out of the final product, contains residual color, the latter may be destroyed by treating the reaction mass with dilute hypochlorite solution or with a decolorizing charcoal.

As typical coupling components useable in the above process may be mentioned:

l-aminonaphthalene-4-sulfonic acid (naphthionic acid); l-aminonaphthalene-5-sulfonic acid, (Laurents acid); l-aminonaphthalene-4,6-disulfonic acid; l-aminonaphthalene-4,7-disulfonic acid; l-aminonaphthalene-4,8-disulfonic acid; l-aminonaphthalene-S,S-disulfonic acid; 2-aminonaphthalene-4-sulfonic acid; 2-aminonaphthalene-6-sulfonic acid, (Broenners acid); 2-aminonaphthalene-3,6-disulfonic acid, (amino-R acid); Z-aminonaphthalene-4,8-disulfcnic acid; Z-aminonaphthalene-5,7-disulfonic acid, (amino-J-acid);

and 2-aminonaphthalene-6,8-disulfonic acid, (amino-G-acid).

Without limiting this invention, the following exam les are given to illustrate my preferred mode of operation. Parts mentioned are by weight.

Example 1 4.5 parts (0.02 mol) of 6-amino-2(p-aminophenyl) benzoxazole were tetrazotized in diluted hydrochloric acid, and the resulting tetrazo compound was coupled with 9.8 parts (0.04 mol) of Broenners acid sodium salt. The acidity was adjusted to slightly acid on Congo Red paper by the addition of sodium acetate. \Vhen the coupling was completed, the mixture was made alkaline to Brilliant Yellow paper by the addition of 30% sodium hydroxide, and the disazo dye was salted out and filtered ofi.

The obtained wet dye was slurried in 200 parts of water at 60 C. A solution of 20 parts of copper sulfate pentain Example 1.

a .le c

hydrate'(CuSO4-5HzO) in 100 parts of water and 120 parts of 28% aqueous ammonia was added. The mixture was then heated to reflux for 24 hours and thereafter filtered hot and washed. The-wet cake was slurried in 600 parts ofdilute hydrochloric acid and the slurry was boiled for 1 hour and filtered hot. The obtained cake "was washed with hot water and slurried in 1000 parts of water. The mixture was made alkaline with sodium hydroxide solution (10%) and heated to obtain solution. After Clarification by heating this solution at about 60 C. with an excess of alkaline solution of sodium hypochlorite, the product was recovered by salting out, filtering and drying. It was a cream colored powder, soluble in water with blue fluorescence; The absorptionmaximurn of this compound in aqueous solution is located at 372 millimicrons. The end product is considered'to have the formula:

' and builds up to a strong white when applied'to cellulosic the boil. The product was recovered from-the filtrate by salting out, filtering and drying. It was a cream colored powder soluble in water with blue fluorescence. The absorption maximum of this compound in aqueous solution is located at 375 millimicrons. The end product is considered to have the formula:

N\ OT E and builds up to a strong white when applied to cellulosic textiles in serial washes in the presence of a soap or de- 7 tergent. I

' 'The starting material, '6-amino-2-(p-aminophenyl) benzoxazole was obtained by heating equal molecular amounts of 5-nitro-2-aminophenol and p-nitrobenzoyl chloride in trichlorobenzene as solvent at 180 to 190" C. for' 3 hours followed by isolation ofthe formed 6-nitro- 2(p-nitrophenyl) benzoxazole. The latter was then reduced according to the process described by Kym, Ber.

32, 1431, (1899), for the preparation of theanalogous 5-amino-2(p-arninophenyl) benzoxafzole.

Example 2 7 a 4.5 parts of 6-amino-2(p-aminophenyl) .benzoxazole were tetrazotized and coupled with 12 parts of the sodium salt of amino-R acid, according to the process described The dye thus obtained'was dissolved in, 200' parts'of water and oxidized as in Example 1. The

reaction mass was filtered. The cake was slurried in water, treated with an excess of sodium sulfide solution (as shown by test with lead acetate paper), boiled a few minutes and filtered hot." The filtrate was decolorized with an aqueous solution of sodium hypochloride, and the product was salted out with sodium chloride. It was a pale tan powder, soluble 'in water with blue fluorescence. The absorption maximum of this compound in-aqueous solution is located at 375 millimicrons. The product i builds up to a strong White when applied to cellulosic textiles in serial Washes in the presence of a soap or detergent.

Example 3 W Y 5.6 parts (0.025 mol) of 6-amino-2(p-aminophenyl) benzimidazole [Kym, 0., Ber. 32, 2180 (1899)] were tetrazotized in dilute hydrochloric acid, and the resulting tetrazo compound was coupled with 12.5 parts (0.05 mol) of napthionic acid sodium salts The further details of coupling and isolation were as in Example 1.

The wet dye was slurried in 500 parts of water at 60 C.

-A solution of 20 parts of CuSOr-SHzO in 100 parts of water and 120 parts of 28% aqueous ammonia was added. The mixture was then heated to reflux for 24 hours and thereafter filtered hot and washed. The wet cake was slurried in 500 parts of dilute hydrochloric :acid (10%) and the slurry was boiled for 1 hour. and filtered hot.

7 The filter cake was washed withlhot water .and slurried in 3000 parts of water. The mixture was made alkaline with sodium hydroxide (10%) and heated. The obtained solution was clarified by treatment with an excess Of. sodium hydrosulfite at about 60 C. and then filtered at slurried in 1000 parts of water.

SOaNa textiles in serial washes the presence of a soap or detergent.

Example 4 5.6 parts (0.025 mol)' 10f -:6=amino 2(p-aminophenyl) benzimidazole were tetrazotized, coupled 'to the sodium salt of Broenner,s acid and the obtained dye was oxidized as in Example 3. The final product was a light tan powder soluble in water with bluish fluorescence. The absorption maximum of this compound in aqueoussolution is located at 373' millimicrons.- Its'properties are similar to those of-the product of Example 3.

g Example 5 2.4 parts 0.01 mol) of 6 -amino-2(p-arninophenyl) benzothiazole were tetrazotized in dilute hydrochloric acid and the resulting .tetraz o compound was coupled with 4.9 parts (0.02 mol) of naphthionie acid sodium salt, and followed by further treatment and isolation as in Example 1.- i V a The obtained wet dye was slurried in 300'parts of water at60 C. A solution of 10 parts of CuSO4-5H2O in parts of water and parts of 28% aqueous ammonia was added. The mixture-was thenheated to reflux for 24 hours and thereafter filtered hot and washed. The wet cake was slurried in 200 parts of dilute hydrochloric acid (10%) and the slurry was boiled for '1 hour and filtered hot. The obtained cake was washed with hot water and After further treatment and isolation as in Example 1, a light yellow powder was obtained, which was soluble intwater with blue fluorescence. The absorption maximum of this compound in aqueous solution is located at 385 millimicrons. The end product is considered to have the formula:

Oa B SOzNa V w and builds up to a strong white when applied to cellulosic fibers in serial washes in the presence of a soap or detergent. r

The starting material; 6-arnino-2-(p-ami! lopheriyll benzothiazole was obtained by' nitrating Z-(p-nitrophenyl) benzothiazole, according to the process described by Bogert, M. T. in I. Am. Chem. Soc. 44, 832 (1922) for the preparation of 6-nitro-2-phenylbenzothiazole. The 6-nitro-2-(p-nitrophenyl) benzothiazole thus obtained was reduced to the desired product by treatment with stannous chloride and hydrochloric acid, as described by Rivier, 1-1., in Helv. Chim. Acta 20, 703 (1937) for the preparation of 6-amino-2-phenylbenzothiazole.

The products obtained in the above examples have been isolated as the sodium salts of the sulfonic acids. By using potassium hydroxide and potassium salts in lieu of sodium hydroxide and sodium salts, throughout, the products may be obtained as potassium sulfonates. Isolation as the free sulfonic acids can be effected by acidification of the condensation mass, and the products thus obtained may be reacted with ammonium hydroxide or any suitable organic or inorganic base, to yield the corresponding salts.

Example 6.M0de of testing The serial washes mentioned in the above examples were carried out as follows:

Cotton cloth was entered into an aqueous bath containing a heavy duty detergent in quantity corresponding to 0.15% of the Weight of the cloth, and 10 parts of the fluorescent agent per million parts of cloth. The heavy duty detergent was a commercial detergent composed, by weight, of approximately of the active ingredient (i. e., a long chain alkyl aryl sulfonate), 2% of carboxy methyl cellulose and 68% of sodium polyphosphate. After stirring at 130 F. for 20 minutes, the cloth was removed from the bath, rinsed and dried. The fluorescence of the cloth thus treated was measured by spectrophotometric methods. Then the same cloth was subjected to four additional, identical treatments.

Several fluorescent agents were tested by this procedure. In separate experiments the total amount of fluorescent agent parts per million parts of cotton) was applied in a single application under otherwise identical conditions.

These tests showed the new products to have very high tine-torial strength, and to give either by the serial washes or in a single treatment a whitening effect comparable to the best products now on the market. Similar excellence of quality were found by tests for substantivit t0 cellulosic fiber and for wash-fastness.

Fabrics washed as above were also subjected to tests to determine the bleach fastness of the fluorescent efiect, and were found to be highly satisfactory in this respect.

The practical merits of my invention will now be readily apparent. The compounds of this invention are suitable for incorporation into soap or synthetic detergents, and endow a fluorescent or whitening eflect to cotton fabric laundered with such soap or detergent. In addition, my novel compounds may also be used fo various other purposes where fluorescence or absorption of ultra-violet light is desirable, for instance to achieve novel effects on photographic paper, as ultraviolet filters when impregnated on cellulosic films which are used for wrapping materials, etc.

I claim as my invention:

1. A compound of the general formula wherein Y designates a member of the group consisting of oxygen, sulfur and the imino radical, X is a sulfo group, while n stands for an integer not greater than 2.

2. A compound of the formula i i' ii Q= =Q wherein R is the 6,4-radical of 2-phenyl-benzoxazole, while each Q is a 1,2-naphthylene radical carrying a sulfo group in the 6-position.

3. A compound for the formula NN--R--NN Q=1\|T N=Q wherein R is the 6,4-radical of Z-phenyl-benzoxazole, while each Q is a 1,2-naphthylene radical carrying sulfo groups in positions 3 and 6.

4. A compound of the formula wherein R is the 6,4'-radical of Z-phenyl-benzimidazole, while each Q is a l,2-naphthylene radical carrying a sulfo group in the 6-position.

5. A compound of the formula at i=3 wherein R is the 6,4-radical of 2-phenyl-benzimidazole, while each Q is a 1,2-naphthylene radical carrying a sulfo group in the 4-position.

6. A compound of the formula lF-NR-N-1fi1' Q= Q wherein R is the 6,4-radical of 2-phenyl-benzothiazole, while each Q is a 1,2-naphthylene radical carrying a sulfo group in the 4-position.

7. The process of producing a fluorescent agent of bluish fluorescence and good bleach-fastness, which comprises coupling a tetrazotized diamine selected from the group consisting of 6-amino-2(p-arninophenyl) benzoxazole, 6-amino-2(p-arninophenyl) benzthiazole and 6- amino-2(p-aminophenyl) benzimidazole to two molecules of an aminonaphthalene sulfonic acid of the formula wherein one of the members Z, Z is NHz while the other one is hydrogen, X is a sulfo group and n is a numeral not greater than 2, and oxidizing the resulting bis-orthoarninoazo compound to produce the corresponding bistriazole.

8. A process as in claim 7, the oxidation being effected by heating the compound in an aqueous solution of cupric-ammonium sulfate.

No references cited. 

1. A COMPOUND OF THE GENERAL FORMULA 